1. Field of the Invention
The present invention relates to an organic light emitting display device, and more particularly, to a lighting test of an organic light emitting display device.
2. Description of Related Art
Recently, there have been developed various types of flat panel display devices having less weight and volume than cathode ray tube display devices.
Among these flat panel display devices, an organic light emitting display device has excellent luminance and color purity by displaying images using organic light emitting diodes (OLEDs) that are self light-emitting devices. Accordingly, the organic light emitting display device has been spotlighted as a next-generation display device.
The organic light emitting display device can be categorized as a passive matrix type organic light emitting display device or an active matrix type organic light emitting display device, depending on a method of driving the OLEDs.
The active matrix type organic light emitting display device includes a plurality of pixels positioned at crossing regions of scan and data lines. Each of the pixels includes an OLED and a pixel circuit for driving the OLED. Because of an advantage of less power consumption, the active matrix type organic light emitting display devices are widely used for portable display devices and the like.
However, in the active matrix type organic light emitting display device, a luminance difference between pixels may occur due to a threshold voltage variation among driving transistors, so image quality may be deteriorated.
Therefore, pixel circuits of various structures have been proposed to compensate for the threshold voltage variation among the driving transistors. For example, a pixel circuit employing a compensation transistor that allows a driving transistor to be diode-connected during a predetermined period is widely known.
Generally, an initialization transistor and a light emitting control transistor are employed together with the compensation transistor in the pixel circuit.
The initialization transistor is employed to allow a data signal to be stably supplied to a pixel when the threshold voltage variation is compensated for by diode-connecting a driving transistor. The initialization transistor initializes a node to which a gate electrode of the driving transistor is connected before a data signal is written in a pixel. That is, the initialization transistor is turned on during an initialization period before a programming period in which the data signal is written in the pixel.
The light emitting control transistor is employed to allow each pixel to stably emit light after performing the initialization and writing of the data signal. For this, the light emitting control transistor is turned on during a light emitting period following the initialization and programming periods.
Here, the initialization period is set to be a period in which a previous scan signal is supplied to a pixel, and the programming period is set to be a period in which a current scan signal is supplied to the pixel. The light emitting period is set to be a period in which the voltage level of a light emitting control signal is set to a low level.
That is, each of the pixels is driven corresponding to the previous and current scan signals and light emitting control signal, which are subsequently shifted and supplied.
Thus, when performing a lighting test for inspecting failures of pixels, three timing signals (a previous scan signal, a current scan signal and a light emitting control signal) should be sequentially supplied to each of the pixels.
A failure test such as a lighting test should be performed in the state that a driving circuit used in actual driving, e.g., a scan driver and/or a light emitting driver, is built in a panel of the organic light emitting display device.
However, in the case that a defect occurs in a built-in circuit, or its characteristic is changed when included in a large-sized panel, it is difficult to repair the built-in circuit. That is, a faulty panel having a built-in circuit in which a defect occurs may not be released as a product and may be scrapped. In this case, module components such as FPC, IC and bonding materials and manufacturing time, which are consumed in the faulty panel, may be wasted.
Therefore, it is desirable that a lighting test is performed in a panel with no built-in circuit, then a driving circuit, for example in the form of an integrated circuit (IC) chip, is installed or mounted on the panel.
However, in the event that no built-in circuit exists, a lighting test may not be performed before the installation of an IC chip.